Kodan for sixth playable race!
Premise
The kodan are one of the friendliest of the current non-playable races, with no major overarching conflict with any other race or faction. Their religious worship of Koda is a good unifying force, and provides motivation for action. (The gods for the humans, the Spirits of the Wild for the norn, the Eternal Alchemy for the asura, loyalty to warbands for the charr, and reverence of the Pale Tree and the Ventari Tablet for sylvari.)
The hometown of the kodan would be situated in the north, together with their polar sanctuaries: Frostgorge Sound, Snowden Drifts & Fireheart Rise. With Heart of Thorns in the west, the events of Orr in the south, and the ley-line fissures converging in the east, they would have safe refuge in their own territory for the foreseeable future.
Character
The kodan are bipedal, humanoid, and would allow for more variety in form of character. Of the current five playable races, norn are similar to humans, and sylvari are halfway there, so another animal-like race would join the likes of the asura and the charr. They are also of suitable hitbox shape and stature, for example compared to other creatures such as the centaurs or the harpies.
The kodan might skew the average size. A sixth race may want to be shorter i.e. between sylvari and asura, but this is assuming that an even distribution of height across the playable races is even on the table. Considering how much shorter the asura are compared to the other four, this might not be the case, and the kodan can stand right up there with the charr.
Gameplay proposals
The personal story begins with an immediate immersion in the culture of the race. For the kodan, a tight community, social structure and strong spiritual beliefs within their close-knit arctic settlements provides a solid starting point for potential exploration and expansion of their territory.
Racial skills are at least partly influenced by the respective religions, and Koda provides a good variety. The Voice, with a deep connection to the Mists, and the Claw, with strong leadership, are possible avatars to transform into as an elite skill. Experiencing the Rage of Koda can be on the auxiliary bar for the avatar forms, or a long-cooldown utility skill. Being polar bears they could probably just heal by turning into a block of ice.
Including the kodan in the playable universe could help to improve variety in armor types. Hopefully the kodan bring their own fur-lined and heavy-set cultural wardrobe. (With knight/ornate armor for humans, gladiator/tribal armor for norn, technological/mechanical armor for asura, brigand/field armor for charr, and plant/nature armor for sylvari.)